U.S. patent number 4,285,319 [Application Number 06/091,755] was granted by the patent office on 1981-08-25 for air flow amount adjusting system for an internal combustion engine.
This patent grant is currently assigned to Nippon Soken, Inc., Toyota Jidosha Kogyo Kabushiki Kaisha. Invention is credited to Tamotsu Fukuda, Tadashi Hattori, Takamichi Nakase, Akira Takata.
United States Patent |
4,285,319 |
Hattori , et al. |
August 25, 1981 |
Air flow amount adjusting system for an internal combustion
engine
Abstract
An air flow amount adjusting system produces an air-fuel mixture
of a desirable air-fuel ratio by controlling the direction of
movement of a bypass valve mounted in an additional air supply pipe
adapted to supply additional air into either the intake system or
exhaust system of an internal combustion engine in accordance with
an output signal produced from a gas sensor mounted in the exhaust
system of the engine and indicative of the air-fuel ratio of the
mixture supplied to the engine. A two-level mode signal whose
threshold corresponds to the desired air-fuel ratio is produced in
accordance with the output signal of the gas detector. After the
two-level mode signal has changed from one level to the other
level, the movement of the bypass valve is stopped for a certain
period of time. If desired, the stopping period of the bypass valve
may be changed in accordance with the temperature of the
engine.
Inventors: |
Hattori; Tadashi (Okazaki,
JP), Takata; Akira (Toyota, JP), Fukuda;
Tamotsu (Toyota, JP), Nakase; Takamichi
(Gamagori, JP) |
Assignee: |
Nippon Soken, Inc. (Nishio,
JP)
Toyota Jidosha Kogyo Kabushiki Kaisha (Toyota,
JP)
|
Family
ID: |
26403585 |
Appl.
No.: |
06/091,755 |
Filed: |
November 6, 1979 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
30953 |
Apr 17, 1979 |
4192268 |
|
|
|
798948 |
May 20, 1977 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
May 28, 1976 [JP] |
|
|
51-62542 |
May 31, 1976 [JP] |
|
|
51-63325 |
|
Current U.S.
Class: |
123/682; 123/700;
60/276; 60/285 |
Current CPC
Class: |
F02D
41/1481 (20130101); F02B 1/04 (20130101) |
Current International
Class: |
F02D
41/14 (20060101); F02B 1/00 (20060101); F02B
1/04 (20060101); F02D 001/04 () |
Field of
Search: |
;123/585,589,489,445,446,531,586,587,588 ;60/276,285 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Nelli; R. A.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Parent Case Text
This is a division of application Ser. No. 030,953, filed Apr. 17,
1979, now U.S. Pat. No. 4,192,268, which is a continuation of Ser.
No. 798,948, filed May 20, 1977, now abandoned.
Claims
What is claimed is:
1. In an additional air supply system for an internal combustion
engine comprising:
a combustion chamber for producing combustion therein;
an intake system operatively communicated with said combustion
chamber for supplying thereto an air-fuel mixture;
an exhaust system operatively communicated with said combustion
chamber for conveying an exhaust gas from said combustion chamber
to the atmosphere;
an additional air supply pipe communicated with at least one of
said intake and exhaust systems for supplying additional air
thereto, thereby controlling the air-fuel ratio of said air-fuel
mixture at a desired value;
air-fuel ratio detecting means disposed in said exhaust system for
detecting the air-fuel ratio of the air-fuel mixture supplied with
said additional air;
control means operatively disposed in said additional air supply
pipe for controlling the amount of the additional air to be
supplied;
drive means operatively connected with said control means for
driving the same; and
a control circuit electrically connected with said air-fuel ratio
detecting means and said drive means for intermittently actuating
said drive means in response to the detected air-fuel ratio;
the improved control circuit comprising:
an air fuel ratio discriminating circuit connected with said
air-fuel ratio detecting means for comparing the output from said
detecting means with a preset level and for generating a high level
or a low level signal based on the comparison;
means for stopping the actuation of said drive means in response to
change of said signal from one level to the other for a period
following a level change to prevent an erroneous operation of said
control means, including a first monostable multivibrator connected
to said discriminating circuit for producing a timing pulse for a
predetermined period following change from a first to a second
level, a second monostable multivibrator connected to said
discriminating circuit for producing a timing pulse for a
predetermined period following change from said second to said
first level, logic means connected to said first and second
multivibrators and said discriminating circuit and connected to
said driving means for causing actuation of said driving means in
accordance with said signal from said discriminating means and
preventing actuation during said timing pulses.
2. A system as in claim 1, wherein said drive means includes a
pulse motor and said logic means includes clock means for producing
clock pulses, a reversible shift register connected to said pulse
motor for causing the field coils of said pulse motor to be
sequentially actuated as said shift register sequentially shifts
its output in response to pulse signals, and gate means connecting
said first and second monostable multivibrators, said clock means
and said discriminating means to said shift register for applying
said clock pulses to said shift register to cause said shift
register to shift its output in a first direction to cause rotation
of said pulse motor when no timing pulse is being produced and said
discriminating means is producing a high level signal and applying
said clock pulses to said shift register to cause said shift
register to shift its output in a second direction to cause
rotation of said pulse motor in the opposite direction when no
timing pulse is being produced and said discriminating means is
producing a low level signal.
3. In a system as in claim 2, further including means for detecting
when said control means is in a fully closed position, and
producing a first signal when said control means is in said fully
closed position and a second signal when said control means is not
in said fully closed position and means for connecting said
detecting means to said gate means for preventing said gate means
from applying clock pulses to said shift register to cause shifting
in said second direction when said detecting means produces said
first signal.
4. In a system as in claim 1 or 2, further including temperature
means for detecting engine temperature and producing a first signal
when said engine is cold and a second signal when said engine has
warmed up and means connected to said first multivibrator and to
said temperature means for decreasing the duration of said timing
pulse produced by said first multivibrator when said first signal
is produced so as to cause operation at a value smaller than the
stoichiometric ratio.
Description
To obtain a maximum efficiency of modified engines which have been
proposed for automobile exhaust emission control purposes or to
ensure an optimum purification of the exhaust gases by the exhaust
gas purifying catalysts mounted in engines for the similar exhaust
gas emission control purposes, the air-fuel ratio of the mixtures
supplied to the engine must always be controlled properly by means
of additional air or alternately the amount of secondary air to the
catalyst must be controlled properly.
The present invention relates to air flow amount adjusting systems
for internal combustion engines which are capable of satisfactorily
meeting the abovementioned requirements.
A system of the above type has been proposed which includes a gas
sensor adapted to detect the air-fuel ratio of the mixture in
accordance with the concentration of oxygen, a constituent, of the
exhaust gases, whereby a bypass valve is continuously operated in
response to the output signal of the gas sensor to control the rate
of flow of correcting additional air and thereby control the
air-fuel ratio of the mixtures.
A disadvantage of this type of system is that due to disturbance or
the like of the exhaust gas stream flowing past the location of the
gas detector, there is the possibility of the gas detector
detecting the localized oxygen content of the exhaust gases in
place of the overall oxygen content causing an erroneous detection
of the air-fuel ratio of the mixture which is correlated with the
oxygen content, with the result that as for example, despite the
fact that the air-fuel ratio of the mixture is large (lean), an
instantaneous pulse-like signal indicative of a small (rich)
air-fuel ratio is generated, and the bypass valve is operated
erroneously.
Another disadvantage is that the gas detectors used are usually of
the type which have a step output characteristic with respect to
the air-fuel ratio of the mixtures as shown in FIG. 2, with the
result that when the air-fuel ratio of the mixtures comes near a
predetermined air-fuel ratio, the detector output is alternately
changed at very short periods, and the direction of movement of the
bypass valve is rapidly changed, thus causing the bypass valve, the
bypass valve support, etc., to wear rapidly and thereby
deteriorating their durability.
The prior art system of the above type generally employs a pulse
motor to serve as a drive unit for operating the bypass valve, and
the air-fuel ratio is generally controlled by holding the operating
speed of the motor constant, that is, the operating speed of the
motor is set at an optimum value which minimizes variation of the
air-fuel ratio both during the steadystate and transient operating
conditions of an engine.
With this prior art system, however, the bypass valve is always
operated continuously, and moreover no consideration is given to
the effect of the delay time factor. Thus, there is a disadvantage
that even if the operating speed of the motor is set at an optimum
value, due to the operating speed being constant, the air-fuel
ratio of the mixtures is varied greatly under the effect of the
delay time factor between the time that the air-fuel ratio of the
mixture is changed by additional air in the intake system and the
time that the exhaust gas constituent is changed and detected by
the gas detector in the exhaust system, and consequently the
control range of the air-fuel ratio is increased, thus making it
impossible to satisfactorily control the air-fuel ratio throughout
a wide range of operating conditions of the engine.
Particularly, during low load and low rotational speed operation
where the amount of intake air is small, the delay time is
increased thus causing a hunting phenomenon and thereby failing to
ensure a full display of the purifying function of the catalytic
converter, and moreover a surging phenomenon is caused during the
running of the vehicle thereby deteriorating the drivability.
With a view to overcoming the foregoing deficiencies, it is an
object of this invention to provide an air flow amount adjusting
system wherein noisy instantaneous pulse-like signals from a gas
sensor disposed in the exhaust system of an engine are eliminated,
and when the air-fuel ratio of the mixture supplied to the engine
reaches a predetermined ratio the operation of means for operating
a bypass valve mounted in an additional air passage is practically
stopped, thereby improving the durability of the bypass valve and
other associated component parts.
This object of the invention is accomplished by stopping the
operation of the bypass valve for a predetermined period of time in
response to a change from one level to the other of the signal from
the gas detector.
It is another object of this invention to provide such air flow
amount adjusting system wherein the said predetermined time period
is varied in accordance with the engine temperature to thereby
control the air-fuel ratio at a desired value.
It is still another object of the invention to provide such air
flow amount adjusting system wherein each time a timing pulse
synchronized with the rotation of the engine is generated, the
additional air amount controlling bypass valve is intermittently
operated a predetermined amount to thereby minimize the variation
of the air-fuel ratio due to the delay time in the engine
system.
It is still another object of the invention to provide such air
flow amount adjusting system wherein during sudden acceleration or
deceleration of an engine, the frequency of timing pulses is
increased to thereby ensure an improved response.
It is still another object of the invention to provide such air
flow amount adjusting system wherein during sudden acceleration or
deceleration of an engine, the amount of movement of the bypass
valve upon each timing pulse is increased over that obtained during
the periods of steady-state operating conditions of the engine,
thereby ensuring an improved response.
The above and further objects and novel features of the present
invention will be more fully understood from the following detailed
description when the same is read in connection with the
accompanying drawings.
It is to be expressly understood, however, that the drawings are
for the purpose of illustration only and are not intended as a
definition of the limits of the present invention.
FIG. 1 is a schematic diagram showing the general construction of
an air flow amount adjusting system for an internal combustion
engine according to the present invention.
FIG. 2 is an output characteristic diagram of the gas sensor shown
in FIG. 1, showing the variation of electromotive force in relation
to the variation of air-fuel ratio.
FIG. 3 is a circuit diagram showing in detail the control unit used
in the first embodiment.
FIG. 4 is a waveform diagram useful in explaining the operation of
the system of this invention in accordance with the control unit
shown in FIG. 3.
FIG. 5 is a circuit diagram showing the principal parts of a
modification of the control unit shown in FIG. 3.
FIG. 6 is a sectional view showing the construction of an
acceleration/deceleration switch used in a second embodiment.
FIG. 7 is a block diagram showing a second embodiment of the
control unit.
FIG. 8 is a detailed circuit diagram for the block diagram shown in
FIG. 7.
FIG. 9 is a waveform diagram useful in explaining the operation of
the system of this invention in accordance with the control unit
shown in FIG. 8.
FIG. 10 is a circuit diagram showing the principal parts of a
modification of the control unit shown in FIG. 8.
FIG. 11 is a circuit diagram showing the principal parts of another
modification of the control unit shown in FIG. 8.
The present invention will now be described in greater detail with
reference to the illustrated embodiments.
Referring first to FIG. 1 showing the entire system of a first
embodiment of the invention, an engine 1 is designed so that it is
supplied with a mixture of air and fuel from a carburetor 2 through
an intake manifold 3. The engine 1 comprises for example an
ordinary four-cycle reciprocal gasoline engine.
In the intake system of the engine 1, a throttle valve 4 is mounted
in the downstream portion of the carburetor 2, and an air cleaner 5
is disposed upstream of the carburetor 2. An additional air passage
6 is disposed to communicate the air cleaner 5 with the carburetor
2 downstream of the throttle valve 4 and bypass the fuel nozzle of
the carburetor 2 and the throttle valve 4.
Also disposed in the exhaust system of the engine 1 are an exhaust
manifold 7, and a catalytic converter 8 incorporating for example a
three-way catalyst, and also mounted in the exhaust manifold 7 is a
gas sensor 9 which employs a metal oxide such as zirconium dioxide
or titanium dioxide to detect the concentration of oxygen, a
constituent, of the exhaust gases and thereby detect the air-fuel
ratio of the mixture which is correlated with the oxygen
concentration.
In the case of the gas detector 9 employing zirconium dioxide, an
electromotive force of about 1 V is produced when a mixture richer
than a stoichiometric air-fuel ratio is supplied to the engine 1,
whereas an electromotive force of about 100 mV is produced when the
mixture supplied is leaner than the stoichiometric ratio, and thus
the output electromotive force of the gas sensor 9 changes
practically in a stepwise manner at around the stoichiometric ratio
as shown in FIG. 2.
A control unit 10 functions to operate a pulse motor 11 in a
selected direction in response to the signals from various
detectors including the gas sensor 9, and the control unit 10
comprises various electronic circuits which will be described
later. The pulse motor 11 functions to open and close a bypass
valve 12 mounted in the additional air passage 6, and its drive
shaft is coupled to the shaft of the bypass valve 12. In this
embodiment, the pulse motor 11 is of the four phase, two-phase
excitation mode type.
The bypass valve 12 is an ordinary square butterfly valve, and it
is positioned in the additional air passage 6. The bypass valve 12
is provided with a valve fully-closed detector switch 13 which
detects that the bypass valve 12 is in its fully closed position,
namely, the switch 13 is turned on when the bypass valve 12 is in
the fully closed position, while the switch 13 is turned off when
the bypass valve 12 is in any other position, and its output signal
is applied to the control unit 10.
Numerals 14 and 15 respectively designate an engine revolution
detector and an acceleration/deceleration switch which are
associated with another embodiment that will be described later,
and therefore these detector and switch will be described in detail
in connection with another embodiment.
Next, the construction of the control unit 10 will be described in
detail with reference to FIG. 3. In the Figure, numeral 10a
designates an air-fuel ratio discriminating circuit for determining
the relative magnitude of the output signal of the gas sensor 9,
and it comprises a voltage comparison circuit including an input
resistor 101, a differential operational amplifier 104 (hereinafter
referred to as an OP AMP) and voltage dividing resistors 102 and
103 for applying a preset voltage to the inverting input terminal
of the OP AMP 104, and the noninverting input terminal of the OP
AMP 104 is connected to the gas sensor 9 through the input resistor
101. The preset voltage determined by the dividing resistors 102
and 103 is set at a value equal to the electromotive force produced
by the gas sensor 9 at around the stoichiometric air-fuel ratio
(V.sub.a in FIG. 2). Consequently, when the air-fuel ratio detected
by the gas sensor 9 is smaller than the stoichiometric ratio or the
mixture is rich as compared with the stoichiometric ratio, a "1"
level signal is generated at an output terminal A of the air-fuel
ratio discriminating circuit 10a, whereas when the detected
air-fuel ratio is greater than the stoichiometric ratio or the
mixture is lean, a "0" level signal is generated at the output
terminal A.
A monostable circuit 10b is designed to generate a timing pulse for
a predetermined period in response to a change in the state of the
output signal of the air-fuel ratio discriminating circuit 10a, and
it comprises an inverter 105, a first monostable multivibrator
including an inverter 116, a resistor 117, a capacitor 118 and an
AND gate 119, a second monostable multivibrator including an
inverter 120, a resistor 121, a capacitor 122 and an AND gate 123,
and a NOR gate 114. Thus, when the output of thee air-fuel ratio
discriminating circuit 10a changes from the "1" level to the "0"
level, the first monostable multivibrator is triggered and
consequently the output of the AND gate 119 goes from the "0" level
to the "1" level for a period of time which is determined by the
resistor 117 and the capacitor 118. On the contrary, when the
output of the air-fuel ratio disciminating circuit 10a changes from
the "0" level to the "1" level, the second monostable multivibrator
is triggered and consequently the output of the AND gate 123 goes
from the "0" level to the "1" level for a period of time determined
by the resistor 121 and the capacitor 122. The outputs of the first
and second monostable multivibrators are added together by the NOR
gate 114, so that the output of the monostable multivibrator 10b
goes to the "0" level for a predetermined time period t as shown in
(B) of FIG. 4 after the output of the air-fuel ratio disciminating
circuit 10a shown in (A) of FIG. 4 has changed its state. On the
other hand, when the output of the air-fuel ratio discriminating
circuit 10a changes its state at a period shorter than the time
period t, the output of the monostable circuit 10b remains at the
"0" level during this time interval.
Numeral 10c designates a clock pulse generating circuit for
generating clock pulses to operate the pulse motor 11, and it
comprises an astable multivibrator including inverters 132 and 134,
a resistor 133 and a capacitor 135 with its output pulse frequency
being selected suitably so as to ensure an optimum control. The
valve fully-closed detector switch 13 comprises a resistor 13a and
contacts 13b, whereby only when the bypass valve 12 is in the
fully-closed position, the contacts 13b are closed and a "0" signal
is generated at its output terminal D. Numeral 10e designates a
command circuit comprising NAND gates 140 and 141 and adapted to
receive the output signals of the air-fuel ratio discriminating
circuit 10a, the monstable circuit 10b and the valve fully-closed
detector switch 13. More specifically, the input terminals of the
NAND gate 140 are respectively connected to the output terminal of
the clock pulse generating circuit 10c, the output terminal B of
the monostable circuit 10b and the output terminal A of the
air-fuel ratio discriminating circuit 10a, and its output terminal
is connected to an input terminal P of a reversible shift register
10f. The input terminals of the NAND gate 141 are respectively
connected to the output terminal of the clock pulse generating
circuit 10c, the output terminal B of the monostable circuit 10b,
the output terminal D of the valve fully-closed detector switch 13
and the output terminal A of the air-fuel ratio discrimination
circuit 10a, and the output terminal of the NAND gate 141 is
connected to an input terminal C of the reversible shift register
10f.
When pulse signals are applied to the input terminal P of the
reversible shift register 10f, its output terminals Q.sub.1,
Q.sub.2, Q.sub.3 and Q.sub.4 are sequentially shifted in this
order, whereas when the pulse signals are applied to the input
terminal C the output terminals Q.sub.4, Q.sub.3, Q.sub.2 and
Q.sub.1 are sequentially shifted in this order. The output
terminals Q.sub.1, Q.sub.2, Q.sub.3 and Q.sub.4 are connected to a
switching circuit 10g comprising resistors 142, 143, 144 and 145,
transistors 146, 147, 148 and 149 and back electromotive force
absorbing diodes 150, 151, 152 and 153, and this switching circuit
10g is in turn connected to field coils C.sub.1, C.sub.2, C.sub.3
and C.sub.4 of the four-phase pulse motor 11. Consequently, when
the pulse signals are applied to the input terminal P of the
reversible shift register 10f, the transistors 146, 147, 148 and
149 are sequentially turned on and the field coils C.sub.1,
C.sub.2, C.sub. 3 and C.sub.4 of the pulse motor 11 are
sequentially energized, thus rotating the pulse motor 11 in the
direction of the arrow in FIG. 3. In response to the rotation of
the pulse motor 11 in the direction of the arrow, the bypass valve
12 is operated in a direction which opens it. On the contrary, when
the pulse signals are applied to the input terminal C, the pulse
motor 11 is rotated in a direction opposite to the direction of the
arrow and consequently the bypass valve 12 is operated in a
direction which closes it.
The control unit 10 and the pulse motor 11 are supplied with power
from a battery 201 through a switch 200 which is operatively
associated with the key switch of the engine 1.
With the construction described above, the carburetor 2 serves the
ordinary fuel measuring function, and it does not differ from the
known carburetors except that it has been adjusted to produce a
mixture of an air-fuel ratio which is slightly rich in fuel as
compared with the desired ratio of air to fuel which is to be
controlled and obtained. The regular main air is mixed with the
corresponding amount of fuel and supplied to the engine 1 through
the main passage of the carburetor 2 and through the intake
manifold 3. After the completion of the combustion in the engine 1,
the exhaust gases are discharged to the atmosphere by way of the
exhaust manifold 7, the catalytic converter 8 and the muffler which
is not shown, and the air-fuel ratio of the mixture supplied to the
engine 1 is detected by the gas sensor 9 mounted in a portion of
the exhaust passage of the exhaust manifold 7. When the
electromotive force produced by the gas sensor 9 is higher than the
preset value V.sub.a, the air-fuel ratio discriminating circuit 10a
discriminates that the air-fuel ratio of the mixture supplied to
the engine 1 is small (rich) and a "1" level signal is generated at
its output terminal A. Consequently, the output of the monostable
circuit 10b goes to the "0" level for the duration of the
predetermined time period t, and the "0" level signal is applied to
the NAND gate 140 of the command circuit 10e. On the other hand,
the "1" level signal from the air-fuel ratio discriminating circuit
10a is inverted by the invertor 105 to a "0" level signal, and this
"0" level signal is applied to the NAND gate 141 of the command
circuit 10e. As a result, both of the NAND gates 140 and 141 are
closed, and the pulse signals from the clock pulse generating
circuit 10c are no longer applied to the reversible shift register
10f, thus causing the pulse motor 11 to stop the movement of the
bypass valve 12. After the time period t, the output of the
monostable circuit 10b goes to the "1" level, and this "1" level
signal is applied to the NAND gate 140. Consequently, the pulse
signals from the clock pulse generating circuit 10b are applied, as
the output signals of the command circuit 10e, to the input
terminal P of the reversible shift register 10f through the NAND
gate 140. As a result, the pulse motor 11 is rotated in the
direction of the arrow so that the opening of the bypass valve 12
is increased and the amount of additional air supplied to the
carburetor downstream of the throttle valve 14 is increased in
accordance with the opening of the bypass valve 12, thus increasing
(leaning out) the air-fuel ratio of the mixture supplied to the
engine 1.
On the other hand, when the air-fuel ratio is increased by the
increased amount of additional air so that the electromotive force
produced by the gas sensor 9 becomes lower than the preset voltage
V.sub.a, the output of the air-fuel ratio discriminating circuit
10a changes its state, thus generating a "0" level signal. Thus,
the bypass valve 12 is stopped by the action of the monostable
circuit 10b for the duration of the predetermined time period t in
the similar manner as mentioned in connection with the opening of
the bypass valve 12, and thereafter a "1" level signal is applied
to the NAND gate 141, thus applying the pulse signals from the
clock pulse generating circuit 10c to the input terminal C of the
reversible shift register 10f. When this occurs, the pulse motor 11
is rotated in the direction opposite to the direction of the arrow,
and the bypass valve 12 is rotated in the direction which closes
it. As a result, the amount of additional air supplied to the
carburetor downstream of the throttle valve 4 is decreased, and the
air-fuel ratio of the mixture supplied to the engine 1 is
decreased.
In this operation, in order to prevent the air-fuel ratio
discriminating circuit 10a from rotating the bypass valve 12
further and bringing it into an "overshoot" position upon failure
of the mixture to attain the desired air-fuel ratio even after the
bypass valve 12 has been moved into its fully closed position, when
the valve fully closed detector switch 13 detects that the bypass
valve 12 is in the fully-closed position, the contacts 13b are
closed so that a "0" level signal is generated and the NAND gate
141 is closed, thus stopping the application of the pulse signals
to the reversible shift register 10f and thereby preventing the
pulse motor 11 from rotating the bypass valve 12 further in the
closing direction thereof. In this way, the bypass valve 12 is
allowed to operate properly.
Next, the control operation of the bypass valve 12 will be
described with reference to FIG. 4. When the output of the air-fuel
ratio discriminating circuit 10a changes its state at a time
t.sub.1 as shown in (A) of FIG. 4, the output of the monostable
circuit 10b goes to the "0" level for the predetermined period t as
shown in (B) of FIG. 4. Consequently, as shown in (C) of FIG. 4,
the movement of the bypass valve 12 is stopped for the duration of
the period t during which its opening is held constant, and
thereafter the bypass valve 12 is operated in the closing
direction.
In the event that the gas sensor 9 makes an erroneous detection of
the oxygen concentration so that the air-fuel ratio discriminating
circuit 10a generates an instantaneous pulse at a time t.sub.2 as
shown in (A) of FIG. 4, the movement of the bypass valve 12 is
stopped for the duration of the period t by the action of the
monostable circuit 10b, thus preventing the occurrence of an
erroneous operation in which the direction of movement of the
bypass valve 12 is changed and the valve is operated to open.
On the other hand, when the air-fuel ratios of the mixtures are at
around the predetermined ratio (the stoichiometric ratio) as during
a time period T.sub.1 and the output of the air-fuel ratio
discriminating circuit 10a changes its state at a short period as
shown in (A) of FIG. 4, the output of the monostable circuit 10b is
maintained at the "0" level during this time period as shown in (B)
of FIG. 4, so that the bypass valve 12 is merely stopped and the
valve is neither opened nor closed. Thus, during low speed and low
load operation of the engine 1, the occurrence of a surging
phenomenon due to any excessive supply of additional air is
prevented, and wear of the bypass valve 12 and its supporting
members including the bearings, etc., is reduced thus increasing
their durability.
While, in the above described embodiment, the first and second
monostable multivibrators of the monostable circuit 10b have the
same time constant and hence the same monostable time period t, if
the monostable time period of the first monostable multivibrator is
made longer than that of the second monostable multivibrator, the
opening of the bypass valve 12 is increased on the whole and the
air-fuel ratio of the mixture is controlled at a valve larger
(leaner) than the stoichiometric air-fuel ratio, whereas if the
monostable time period of the first monostable multivibrator is
made shorter than that of the second monostable multivibrator, the
opening of the bypass valve 12 is decreased on the whole and the
air-fuel ratio of the mixture is controlled at a value smaller
(richer) than the stoichiometric air-fuel ratio.
FIG. 5 shows a modification of the monostable circuit 10b. The
monostable circuit 10b shown in FIG. 5 further comprises a resistor
200 whose resistance value is smaller than that of the resistor 117
(the resistor 121), and the time constant of the monostable circuit
10b is changed by selectively inserting the resistors 117 and 200
by means of a warm-up detector 214 in which contacts 214a and 214b
are closed when the engine 1 is cold, whereas the contacts 214a and
214c are closed when the engine 1 has warmed up. In this way,
before and during warm-up operation of the engine 1 the first and
second monostable multivibrators have different time constants,
thus controlling the air-fuel ratio of the mixture at a value
richer than the stoichiometric air-fuel ratio and thereby ensuring
smooth and satisfactory operation of the engine, and after the
engine 1 has warmed up the first and second monostable
multivibrators have the same time constant and the engine is
returned to the normal operation where it is supplied with a
mixture having the stoichiometric air-fuel ratio.
The warm-up detector 214 may comprise a thermo switch which detects
for example the temperature of the cooling water or cylinder block
of the engine 1.
A second embodiment of the invention will now be described. While,
in the first embodiment, the pulse motor is continuously operated
by pulses of a fixed frequency, in the below-mentioned second
embodiment the pulse motor is intermittently operated and the
amount of additional air is controlled by taking the delay time
factor of the engine into account. For this purpose, the control
unit used in this embodiment detects the engine rotational speed
and acceleration or deceleration of the engine.
Referring to FIG. 1 showing the general construction of the system
of this invention, an engine revolution detector 14 generates
signals in synchronism with the crankshaft revolution of the engine
1 or in accordance with the rotational speed of the engine 1,
namely, in this embodiment the intermittent signal from the primary
winding of the ignition coil generally utilized as the ignition
system of the engine 1 is employed, and the output signal of the
engine revolution detector 14 is applied to a control unit 10.
An acceleration/deceleration switch 15 is disposed in the intake
manifold 3, and it is adapted to be turned on and off electrically
in response to changes in the intake manifold vacuum. Namely,
during the periods of acceleration and deceleration operation of
the engine 1 where the intake manifold vacuum changes rapidly, the
switch 15 is turned on and its output signal is applied to the
control unit 10.
The construction of the acceleration/deceleration switch 15 is of
the diaphragm type as shown in FIG. 6. Now referring to the Figure,
the switch 15 includes two chambers 15c and 15d which are defined
by a casing 15a and a diaphragm 15b, and the two chambers are
communicated with each other through an orifice 15e in the
diaphragm 15b. Also back springs 15f.sub.1 and 15f.sub.2 are
respectively mounted in the chambers 15c and 15d to urge the
diaphragm 15b, and the chamber 15c is communicated with the intake
manifold 3. An electrically conductive shaft 15g is securely
attached to the diaphragm 15b, and a contact 15h is formed at the
forward end of the shaft 15g. A slide terminal 15i is disposed so
as to always contact with the shaft 15g, and also terminals 15j and
15k are disposed so as to contact with the shaft 15g at the
predetermined positions thereof. A relay 15 m is operated in
response to engagement and disengagement of the terminal 15g with
the terminals 15j and 15k, so that contacts 15m.sub.1 and 15m.sub.2
are closed in response to the engagement of the terminals, while
the contacts 15m.sub.1 and 15m.sub.3 are closed in response to the
disengagement of the terminals. In this way, the position of the
relay 15m is changed depending on whether the engine 1 is at the
acceleration/deceleration operation.
The engine revolution detector 14 and the acceleration/deceleration
switch 15 constitute a delay time detecting unit for detecting the
delay time factor of the engine 1. The remaining parts of the
second embodiment shown in FIG. 1 are the same as described in
connection with the first embodiment.
Next, the construction of the control unit 10 will be described
with reference to FIG. 7 showing its block diagram. The control
unit 10 receives as its input signals the output signal of the gas
sensor 9 or an air-fuel signal corresponding to the oxygen content
of the exhaust gases which is closely related with the air-fuel
ratio of the mixture, the output signals of the engine revolution
detector 14 and the acceleration/deceleration switch 15
constituting the delay time detecting unit and the output signal of
the valve fully-closed detector switch 13. The control unit 10
comprises an air-fuel ratio discriminating circuit 10a for
discriminating the air-fuel ratio signal from the gas sensor 9, a
timing pulse generating circuit 10b for generating timing pulses of
a period corresponding to the delay time factor of the engine 1, an
oscillator circuit 10c for generating clock pulses of a
predetermined frequency, a driving pulse circuit 10d responsive to
the timing pulse and the clock pulses to generate driving pulses
for driving the pulse motor 11, a command circuit 10e for
performing the logical operation on the output signals of the
air-fuel ratio discriminating circuit 10a and the driving pulse
circuit 10e, a reversible shift register 10f whose output signals
are sequentially shifted in response to the signals from the
command circuit 10e, and a power circuit 10g responsive to the
output signals of the reversible shift register 10f to control the
energization of the pulse motor 11, thereby causing the pulse motor
11 to operate properly.
The control unit 10 will now be described in greater detail with
reference to FIG. 8. The air-fuel ratio discriminating circuit 10a
comprises an input resistor 101, voltage dividing resistors 102 and
103 and a differential operational amplifier 104 (hereinafter
referred to as an OP AMP), and the OP AMP 104 has its noniverting
input terminal connected to the gas sensor 9 through the input
terminal 101 and its inverting input terminal connected to the
voltage dividing point of the dividing resistors 102 and 103. The
output signal of the gas sensor 9 is compared with a preset voltage
V.sub.a determined by the dividing resistors 102 and 103 (the
voltage equal to the electromotive force produced by the gas sensor
9 at around the stoichiometric air-fuel ratio), whereby a "1" level
output is generated at an output terminal B.sub.1 of the air-fuel
ratio discriminating circuit 10a when the output signal of the gas
sensor 9 is higher than the preset voltage or the mixture is richer
than the stoichiometric air-fuel ratio, whereas a "0" level output
is generated at the output terminal B.sub.1 when the output signal
of the gas sensor 9 is lower than the preset voltage or the mixture
is leaner than the stoichiometric air-fuel ratio, and a signal
opposite to the output at the terminal B.sub.1 is generated at an
output terminal B.sub.2. The timing pulse generating circuit 10b
comprises a reshaper circuit including resistors 106, 108 and 109,
a capacitor 107 and a transistor 110, a binary counter 111, a first
differentiated pulse circuit including an inverter 112, a resistor
113, a capacitor 114 and an AND gate 115, a second differentiated
pulse circuit including an inverter 116, a resistor 117, a
capacitor 118 and an AND gate 119, a third differentiated pulse
circuit including an inverter 120, a resistor 121, a capacitor 122
and an AND gate 123, AND gates 125 and 126, D-type flip-flops 128
and 127, AND gates 129 and 130, an OR gate 131, wand inverters 127a
and 128a.
The pulse signals at the primary winding of the ignition coil
constituting the engine revolution detector 14 are reshaped by the
reshaper circuit and then subjected to frequency division by the
binary counter 111. The frequency dividing ratio is determined by
the acceleration/deceleration switch 15, and in this embodiment it
is so preset that an output Q.sub.1 (the output divided by 2) is
generated at acceleration or deceleration operation of the engine
1, and an output Q.sub.3 (the output divided by 8) is generated
during any other operation of the engine 1. The first
differentiated pulse circuit produces from the frequency divided
output of the binary counter 111 positive differentiated pulses as
shown in (A) of FIG. 9.
It will be seen from the foregoing that these differentiated pulses
or timing pulses are generated in synchronism with the rotation of
the engine and have a period inversely proportional to the engine
rotational speed, and the period of timing pulses during periods of
acceleration and deceleration becomes 1/4 the period obtained
during periods of normal operation. The second and third
differentiated pulse circuits receive as their input signals the
outputs of the air-fuel ratio discriminating circuit 10a, so that
the second differentiated pulse circuit generates positive
differentiated pulses as shown in (C) of FIG. 9 when the output at
the terminal B.sub.1 of the air-fuel ratio discriminating circuit
10a changes from the "0" level to the "1" level (when the mixture
is richer), and the third differentiated pulse circuit generates
positive differentiated pulses as shown in (D) of FIG. 9 when the
output at the terminal B.sub.2 of the air-fuel ratio discriminating
circuit 10a changes from the "0" level to the "1" level (when the
mixture is leaner).
The AND gates 125 and 126 receive the outputs of the first
differentiated pulse circuit and the air-fuel ratio discriminating
circuit 10a as gate input signals, so that when the output at the
terminal B.sub.1 of the air-fuel ratio discriminating circuit 10a
goes to the "1" level, the AND gate 125 is opened and the
differentiated pulses from the first differentiated pulses are
passed as shown in (E) of FIG. 9, and when the output at the
terminal B.sub.2 of the air-fuel ratio discriminating circuit 10a
goes to the "1" level, the AND gate 126 is opened and the
differentiated pulses from the first differentiated pulse circuit
are passed as shown in (F) of FIG. 9.
The D-type flip-flops 127 and 128 have their set terminals S
grounded and their delay terminals D connected to the power source,
and the D-type flip-flop 127 receives as its input signals the
output of the second differentiated pulse circuit at its reset
terminal R and the output of the AND gate 125 at its clock terminal
CL through the inverter 127a. The D-type flip-flop 128 receives as
its input signals the output of the third differentiated pulse
circuit at its reset terminal R and the output of the AND gate 126
at its clock terminal CL through the inverter 128a.
Each of the D-type flip-flops 127 and 128 is so designed that the
output Q is reset to the "0" level when a "1" level reset signal is
applied to the reset terminal R, and the output Q changes from the
"0" level to the "1" level when the input at the clock terminal CL
goes from the "0" level to the "1" level. Thereafter, even if the
input signal at the clock terminal changes its state, the output Q
remains at the "1" level unless a "1" level reset signal is applied
to the reset terminal R.
Consequently, the output Q (at a terminal G) of the D-type
flip-flop 127 becomes as shown in (G) of FIG. 9 in response to the
outputs of the second differentiated pulse circuit and the AND gate
125 shown respectively in (C) and (E) of FIG. 9, and the output Q
(at a terminal I) of the D-type flip-flop 128 becomes as shown in
(I) of FIG. 9 in response to the outputs of the third
differentiated pulse circuit and the AND gate 126.
The outputs of the D-type flip-flops 127 and 128 are respectively
subjected, along with the outputs E and F of the AND gates 125 and
126, to the logical operation by the AND gates 130 and 129, so that
the resulting output H of the AND gate 130 becomes as shown in (H)
of FIG. 9, and the resulting output J of the AND gate 129 becomes
as shown in (J) of FIG. 9.
In other words, when the output signal of the air-fuel ratio
discriminating circuit 10a changes from one level to the other
level, the D-type flip-flop 127 or 128 is reset to the "0" level,
after which the output of the D-type flip-flop 127 or 128 is
changed to the "1" level in response to the change from "1" to "0"
of the first differentiated pulse generated from the first
differentiated pulse circuit in synchronism with the rotation of
the engine, and consequently the AND gate 130 or 129 cancels the
first differentiated pulse generated after the output signal of the
air-fuel ratio discriminating circuit 10a has changed from one
level to the other level. When the output signal of the air-fuel
ratio discriminating circuit 10a thereafter remains unchanged, the
second differentiated pulse et seq. are inverted and passed through
the AND gate 130 or 129.
The OR gate 131 performs the logical operation on the outputs of
the AND gates 130 and 129, so that the AND gate outputs shown in
(H) and (J) of FIG. 9 are superposed one upon another and
consequently the output of the OR gate 131 becomes as shown in (K)
of FIG. 9.
However, if the output of the air-fuel ratio discriminating circuit
10a changes from "0" to "1" or from "1" to "0" during the one cycle
period of the timing pulses shown in FIG. 9, the first timing pulse
after the change has taken place is cancelled, and when the period
of change in the output of the air-fuel ratio discriminating
circuit 10a becomes longer than the period of timing pulses, the
timing pulses are passed through the OR gate 131.
The oscillator circuit 10c comprises inverters 132 and 134, a
resistor 133 and a capacitor 135, and it produces basic clock
pulses for driving the pulse motor 11.
The driving pulse circuit 10d comprises an R-S flip-flop including
NOR gates 136 and 137, a NOR gate 138 and a decade counter 139.
When a "1" level differentiated pulse is applied to a reset
terminal R of the decade counter 139, its outputs Q.sub.0 to
Q.sub.9 are all reset to the "0" level. The counting occurs each
time the clock pulse applied to its carry-in terminal CI changes
from the "0" level to the "1" level, and the output is generated
one at a time at Q.sub.0, Q.sub.1, . . . and Q.sub.9. In this
embodiment the decade counter 139 is of the type which completes
its counting after counting to the base 10, and a "1" level signal
is generated at its carry-out terminal CO upon completion of the
counting. The R-S flip-flop is designed so that the NOR gate 136 is
triggered by the timing pulse from the timing pulse generating
circuit 10b so that the output of the NOR gate 136 goes to the "0"
level and the NOR gate 138 is opened, thus applying the clock
pulses from the oscillator circuit 10c to the carry-in terminal CI
of the decade counter 139. At the same time, the decade counter 139
is reset by the timing pulse and thus the decade counter 139 starts
its counting operation in response to the application of the timing
pulse. When the decade counter 139 counts i clock pulses, its
Q.sub.i output goes to the "1" level, and the NOR gate 137 of the
R-S flip-flop is triggered. Consequently, the output of the NOR
gate 136 goes to the "1" level and the NOR gate 138 is closed, thus
causing the decade counter 139 to stop counting.
As a result, as shown in (L) of FIG. 9, i clock pulses are
generated as the output of the NOR gate 138 in response to each
timing pulse, that is, a certain number of driving pulses are
generated during each predetermined time interval. In this
embodiment, the number of driving pulses generated is preset at an
optimum value so that the control range of air-fuel ratio is
reduced during the periods of both steady-state conditions and
transient conditions. The driving pulses shown in (L) of FIG. 9 are
applied to the command circuit 10e, and consequently the pulse
motor 11 is operated in response to the signals from the air-fuel
ratio discriminating circuit 10a in the similar manner as in the
case of the previously described first embodiment.
The operation of the second embodiment of the invention described
so far with reference to FIGS. 1 and 6 to 8, particularly the
operation of the bypass valve 12 will now be described with
reference to FIG. 9.
The timing pulse generating circuit 10b generates timing pulses as
shown in (A) of FIG. 9 in response to the signals from the engine
revolution detector 14 and the acceleration/deceleration switch 15.
Although not shown, it is so arranged here that during the periods
of acceleration and deceleration operation, the period of timing
pulses is reduced to about 1/4 of the period obtained during the
periods of normal operation, though it is dependent on the
rotational speed of the engine 1.
On the other hand, shown in (B.sub.1) of FIG. 9 is the output
B.sub.1 of the air-fuel ratio discriminating circuit 10a adapted to
discriminate the output signal of the gas sensor 9 which varies
with variation in the air-fuel ratio of the mixtures produced in
the carburetor 2.
Thus, the direction of rotation of the pulse motor 11 is determined
by the air-fuel ratio signal shown in (B.sub.1) of FIG. 9, and the
driving timing and driving time period (driving angle) are
determined by the driving pulses shown in (L) of FIG. 9, thus
driving the pulse motor 11 intermittently. This operation is shown
in terms of the opening of the bypass valve 12 by the broken line I
in (M) of FIG. 9, and it will be seen from (M) of FIG. 9 that the
pulse motor 11 is operated for predetermined time periods in
synchronism with the rotation of the engine, and that the bypass
valve 12 is temporarily stopped during other time periods.
Thus, in accordance with the second embodiment, the pulse motor 11
is operated through a predetermined angle during a predetermined
time period in response to each timing pulse, and the pulse motor
11 is temporarily stopped during other time periods, thus
performing this operation repeatedly. As a result, the amount of
additional air supplied to the intake manifold 3 from the
additional air passage 6 is increased and decreased
intermittently.
This makes it possible to increase the driving speed (the slope of
the broken line I in (M) of FIG. 9) of the bypass valve 12 by the
pulse motor 11, thus improving the response of the bypass valve 12
and making the variation of the air-fuel ratio of the mixtures
small.
Further, in accordance with the second embodiment, during the
transient conditions such as the periods of acceleration and
deceleration where there occurs a sudden change in the amount of
intake air, the period of timing pulses is reduced to about 1/4 the
period obtained during the periods of normal operation thereby
greatly reducing the operating cycle of the pulse motor 11, with
the result that the opening of the bypass valve 12 is rapidly
changed and the air-fuel ratio of the mixture is rapidly returned
to the desired air-fuel ratio.
Still further, in accordance with the second embodiment, where the
engine rotational speed is high and the amount of intake air is
large, the period of timing pulses is decreased in proportion to
the engine rotational speed, so that the operating cycle of the
pulse motor 11 is decreased and the opening of the bypass valve 12
is changed rapidly, thus rapidly returning the air-fuel ratio of
the mixture to the desired ratio without the air-fuel ratio being
varied greatly by the delay time factor of the engine 1. On the
contrary, where the engine rotational speed is low and the amount
of intake air is small, the operating cycle of the pulse motor 11
is increased and the opening of the bypass valve 12 is changed
slowly on the whole, thereby complying with the increase in the
delay time of the engine 1. In this way, the possibility of
excessive additional air supply in the low engine speed range is
eliminated and the variation in the air-fuel ratio of the mixtures
is decreased, thus preventing the occurence of a surging phenomenon
of the engine 1.
By thus driving and stopping the pulse motor 11 intermittently with
timing pulses having a period corresponding to the delay time of
the engine 1 and by repeating this operation, the amount of
additional air can be controlled properly throughout a wide range
of the engine operating conditions.
Still further, in accordance with the second embodiment, even if
the air-fuel ratio discriminating circuit 10a generates an
instantaneous pulse or where the air-fuel ratios of the mixtures
are at around the predetermined air-fuel ratio (the stoichiometric
ratio) thus causing the output of the air-fuel ratio discriminating
circuit 10a to change from one level to the other level and vice
versa at short periods as shown in the region T of FIG. 9, the
pulse motor 11 will not be operated unless the output of the
discriminating circuit 10a remains at the same level for the
duration of a time period during which are generated at least two
of the timing pulses shown in (A) of FIG. 9, thus maintaining the
bypass valve 12 stationary. Consequently, the bypass valve 12 is
prevented from mulfunctioning or the direction of movement of the
bypass valve 12 is prevented from being changed at short cycles,
thereby ensuring stable control of the air-fuel ratio of the
mixtures.
Of course, when the air-fuel ratio of the mixture deviates from the
predetermined ratio, as mentioned previously, the bypass valve 12
is operated in response to each timing pulse, thus changing the
opening of the bypass valve 12 and thereby satisfactorily and
stably controlling the air-fuel ratio at the predetermined
ratio.
While, in the second embodiment, the period of timing pulses is
changed during the periods of acceleration and deceleration by the
binary counter 111 constituting a frequency divider, the same
effect may be obtained by using a driving pulse generating circuit
10d' whose principal parts are shown in FIG. 10. This circuit
differs from the driving pulse generating circuit 10d of FIG. 8 in
that there is further provided a decade counter 154 having its
carry-in terminal CI and reset terminal R respectively connected to
the carry-out terminal CO and the reset terminal R of the decade
counter 139, and the outputs of the decade counters 139 and 154 are
selectively delivered by the acceleration/deceleration switch
15.
With this construction, while the period of timing pulses is not
changed during the periods of acceleration and deceleration, the
number of clock pulses generated in response to each timing pulse
is selected to be either 0 to 9 or 10 to 99, and consequently the
duty cycle of driving pulses is changed, thus changing the driving
time period of the pulse motor 11 and thereby rapidly changing the
opening of the bypass valve 12 during the periods of acceleration
and deceleration.
Further, while, in the second embodiment, the number of clock
pulses generated from the driving pulse generating circuit 10d in
response to each timing pulse is the same and hence the driving
time period is the same for both opening and closing the bypass
valve, it is possible to use a driving pulse generating circuit
10d" whose principal parts are shown in FIG. 11. This circuit
differs from the driving pulse generating circuit 10d of FIG. 8 in
that there are further provided NOR gates 155, 156 and 159, an R-S
flip-flop including NOR gates 157 and 158 and a decade counter 160,
with the NOR gate 155 being connected to the output terminal K of
the timing pulse generating circuit 10b and the terminal B.sub.2 of
the air-fuel ratio discriminating circuit 10a and the NOR gate 156
being connected to the output terminal K and the terminal B.sub.1
of the air-fuel ratio discriminating circuit 10a, whereby the
decade counter 139 determines the number of driving pulses for
closing the bypass valve, and the decade counter 160 determines the
number of driving pulses for opening the bypass valve.
With this construction, the number of clock pulses produced in
response to each timing pulse for opening the bypass valve differs
from that for closing the bypass valve and consequently the rate of
change for opening the bypass valve differes from that for closing
the bypass valve, thus controlling the air-fuel ratio of the
mixture at a value other than the stoichiometric ratio.
Consequently, if, as shown in FIG. 11, a warm-up sensor 17 (e.g.,
an engine cooling water temperature sensor) adapted for switching
in accordance with the warm-up condition of the engine 1 is
provided to change the output of the decade counter 160, during the
warming up period the air-fuel ratio of the mixture can be
controlled at a value smaller than the stoichiometric ratio to
thereby ensure a stable warm-up operation. In this case, the decade
counter is preset in such a manner that Qi.sub.1 =Qi.sub.3
>Qi.sub.2. Of course, the desired air-fuel ratio can be suitably
changed depending on the setting of the decade counter.
The present invention is not intended to be limited to the
above-described embodiments. For example, while, in the
above-described embodiments, the present invention has been shown
as applied to an air flow amount adjusting system for controlling
the air-fuel ratio of the mixtures produced in the carburetor, the
present invention may also be applied to a system designed to
compensate the air flow in mechanically controlled or
electronically controlled fuel injection systems.
Further, in addition to controlling the flow rate of air in the
intake system, the present invention may be applied to a system
designed to control the flow rate of air in the exhaust system,
e.g., the control of the amount of secondary air to the
catalyst.
Still further, while the drive unit comprises a pulse motor, any of
DC or AC motors may be employed or alternately any of mechanical
actuators may be employed in addition to electrical actuators.
Still further, while the delay detecting means comprises the engine
revolution detector 14 and the acceleration/deceleration switch 15,
detectors for detecting other delay time factors such as intake
manifold vacuum, intake air amount, venturi vacuum, throttle angle,
vehicle speed, etc., may be employed singly or in any combination
thereof.
If the detector used is one whose output varies analogically, the
period of timing pulses may be changed analogically by for example
a voltage-to-frequency converter in place of the frequency
divider.
It will thus be seen from the foregoing that the present invention
has among its great advantages the fact that during the
steady-state conditions of an engine, a constituent of the exhaust
gases is detected to thereby control the amount of additional air
throughout a wide range of the engine operating conditions by
taking the delay time factor into consideration. Another advantage
is that since malfunctioning of the bypass valve 12 can be
prevented, if the invention is applied to the control of the
air-fuel ratio of the mixtures, there is a great effect of reducing
the variation of the air-fuel ratio and maintaining the air-fuel
ratio substantially constant and thereby ensuring effective
utilization of the engine exhaust purifying catalyst. Still another
advantage is that the occurrence of surging phenomenon during low
load and low speed operation can be eliminated thus ensuring
improved driveability.
* * * * *